1. Field of the Invention
The invention relates to a composite pipe and a method of manufacturing same.
2. Background Art
Composite pipes having substantially smooth ends, whether spigots or sockets, are known for instance from U.S. Pat. No. 5,472,659 or EP 0 385 465 B1. The smooth ends, which are produced by the joining and welding of two co-extruded tubes, are formed into sockets by subsequent expansion on a socketing machine. This socketing is comparatively convenient to carry out as long as the composite pipes consist of PVC-U. When polyolefins are used, the socketing, i.e. expanding the spigots or the socket portions not yet expanded, is very difficult. Owing to the partially cristalline material structure of polyolefins, the latter exhibit a so-called memory effect. To solve these problems, AT 398 725 B proposes first to expand such a socket beyond its nominal dimension and then to compress it slightly below its nominal dimension, the memory effect thereby being compensated.
When PVC-U is used as a material for the composite pipes, there is no distinct creeping process, which is however very distinct in the case of polyolefins as a material for composite pipes. Consequently, with such composite pipes of polyolefin, there is the risk that the respective socket expands under the action of the seal bearing against it from inside, the pipe connection thereby becoming leaky.